Jökull - 01.12.1990, Side 105

Figure 3. A photo of core no. 3 at the border of
the 1986-1987 and 1987-1988 precipitation layers
(see Fig. 6). Note the ice lenses at the top of the
1987-86 layer. —Ljósmynd af 3. Kjarna á mörkum
Slyólagannafrá 1986-1987og 1987-1988. Takið eftir
íslinsunum efst í snjólaginufrá 1986-1987.
tig. 1986). This data base (the Icelandic Meteorolog-
ical Office, 1958-1981; Gíslason, 1985; Gíslason and
Rettig, 1986) has been used to determine the average
PH and the ratios of major ions in Icelandic precipita-
tion (Gíslason et al., 1990). Individual analyses were
accepted if the difference between the equivalent plus
and minus charges was less than 25% for equations
• and 2 (see below). The number of accepted sam-
Ples is 338. A frequency diagram for the pH of the
Precipitation is shown in Fig. la. The samples show
a near normal distribution around a mean pH of 5.4
with a standard deviation of 0.46. The pH of pure
water saturated with the CO2 of the atmosphere at 0
°C and then heated up to 25 °C without any loss of
gas is 5.5, but the pH of pure water in equilibrium
with the atmosphere at 25°C is 5.7. Thus, the average
precipitation in Iceland is slightly acid compared to
pure water. This might be due to some of the ”excess
sulfur“ content of precipitation in Iceland (Fig. lf).
Plots of Cl- versus the other major ions in Ice-
landic precipitation (Gíslason et al., 1990) are shown
in Figs. lb-f. The lines that are drawn on the dia-
grams are the ratios of the given ions to Cl- in mean
ocean water (Riley and Chester 1971). The Na+/Cl-,
K+/C1- and Mg2+/Cl- ratios in Icelandic precipita-
tion are close to the oceanic ones (Fig. 1), indicating
a primary marine source (marine aerosol) for these
ions in Icelandic precipitation. The concentration of
Ca2+ and SO42- in Icelandic precipitation is greater
than would be predicted from an unfractionated ma-
rine contribution. This is similar to what has been
found elsewhere for sulfur (e.g. Clausen and Lang-
way, 1989) and is partly due to the release of SO2
into the atmosphere by the buming of fossil fuel. In
order to linearly regress the data shown in Figs. le
and lf, a constant enrichment which is independent
of the amount of the marine contribution, is assumed.
The enrichment (pollution) is then represented by the
intercept but the slope of the line is due to the marine
contribution (Figs. le - f). However, it is likely that
some of this excess concentration is brought about by
a local source, thus, especially in remote parts of the
island, this excess Ca2+ and SO42- in Icelandic pre-
cipitation might be much smaller than the intercepts
in Figs. le and lf indicate. Sigurðsson and Einars-
son (1988) have shown the amount of oceanic aerosol
to be greatest close to the coast and to decrease in-
land with increased elevation as demonstrated by their
chloride map of groundwaters in Iceland. From Cl-
analyses of Icelandic precipitation one can predict its
major ion concentration from the linear equations in
Figs. lbto lf. Furthermore,ifonedoesnothaveaCl-
analysis of the precipitation of interest, one can calcu-
late the average composition by obtaining the average
Cl- concentration from the Cl- map of Sigurðsson
and Einarsson (1988) and using the linear equations
JÖKULL, No. 40, 1990 101